Magnetic brake



06L 19, 1937. Q c, FARMER 2,096,486

MAGNETICKBRAKE Filed Feb. 25, 1955 INVENTOR .CLYDE QFARMER.

ATTORNEY Patented Get. 19, 1937 MAGNETIC BRAKE Clyde 0. Farmer, Pittsburgh, Pa., assignor to The Westinghouse Air Brake Company, Wilmerding, Pa", a corporation of Pennsylvania Application February 23, 1925, Serial No. 7,747

2 :Claims.

This invention relates to the typeof railway brake in which a magnetic brakeshoe is normally held suspended above the rail and is adapted to be moved into engagement with the rail. 7

r In one type of magnetic brake system heretofore in use the brake shoe has been suspended above the rail andhas been moved to a position a short distance above the rail. The winding of the shoe was then energized and the magnetic attraction of the shoe for the rail caused the shoe -to move into'engagement with the rail. The

track shoe was secured to the vehicle in such a manner that a limited amount of movement was permitted the shoe longitudinally of the car, and, when the shoe was moved into engagement with the track the shoe tended to seize the rail and to remain stationary relative to the rail and topermit the vehicle to move relative to the shoe until the limit of this movement was reached.

As the coefficient of friction between a shoe and the. rail is relatively high when the shoe is stationary relative to the rail a sudden resistance lwas offered to movement of the vehicle when the limit of movement between the vehicle and the shoe was reached.

Thiscondition was aggravated when the-track was worn so that the clearance between the shoe and the rail at the time the shoe had reached the position to which it was moved by the fluid pressure devices or other means employed to move the shoe. Because of the distance between the shoe and the rail the flux in the shoe'had to build up to a very highvalue before the magnetic attraction between the shoe and the rail was sufficient to cause the shoe to move into engagement with the rail. When the shoe did move' into engagement with the rail theshoe was held in engagement with the rail withgreat force because of the relatively high flux density in the shoe, so thatthe force of friction between the shoe and the rail was relatively high, with the result that the brake took effect suddenly and with a severe jerk.

In another type of brake system employing magnetic track brake shoes the shoes have been moved into engagement with the track by means of fluid pressure devices, but this has not been 1 satisfactory as movements of the track shoe as a 0 result of irregularities in the track were trans mitted to the vehicle through the fluid pressure devices. i

' In addition in'this system when the track shoe was moved into engagement with the track, the

pressure of the fluid in the fluid-pressure devices built up and tended to lift the vehicle away from the rails.

Itis an object of this invention to provide an improved brake system of the type employing .magnetic track brake shoes.

It is another object of this invention to provide an improved braking systemof the type employ ing magnetic track brake shoes and having means to yieldingly press the track brake shoes into engagement with the rail.

It is a further object of this invention to provide an improved braking system employing magnetic track brake shoes andhaving fluid pressure responsive means to yieldingly press the track brake shoes into engagement with the rail, while at the same time employing means responsive to the pressure of the fluid supplied to the fluid pressure responsive means to control the supply of current to the track brake shoe. 7

Other objects of the invention and features of novelty will be apparent from the following description taken in connection with the accompanying drawing, the single figure of which is a diagrammatic sectional View of a magnetic brake apparatus embodying my invention.

As shown in the drawing the apparatus may comprise a magnetic brake shoe I having a suitable winding (not shown) associated therewith and being held suspended above the rail 2 by springs 4 secured to brackets 5 attached to the vehicle truckframe 3. The springs 4 are strong enough to normally maintain the brake shoe 1 outof engagement with the rail 2.

.Means is provided for moving the brake shoe into engagement with the rail, and as shown in the drawing, this means comprises a pressure cylinder 6 containing a movable abutment in the form of a piston 1 to which is secured a rod 8. The lower end of the rod 8 has an en-, larged head 9 formed thereon which is positioned in the spring cage It in engagement with a compression spring II, mounted within the cage ill. The lower portion of the cage II! has a rod l2 secured thereto which is pivotally secured to the brake shoe I. by means of a pin I3.

During the time the air cylinder is vented the .springs 4 are of sufficient strength to support 'the track shoe l above the rail. When it is desired to apply the magnetic track shoe fluid under pressure is supplied to the cylinder 6,

through the pipe 15, ,to which pipe fluid under pressure may be supplied and released by any suitable controlling means. The pressure of the fluidacting upon the'abutmentor piston I forces it downwardly, and its movement is transmitted through the spring I I to the cage I0 and the rod I2 to the brake shoe I to press the brake shoe into engagement with the rail 2. The spring II through which the fluid pressure responsive means operates is of sufiicient strength to force the track shoe downwardly against the resistance of the supporting springs 4.

The abutment or piston I is preferably proportioned so that the fluid pressure supplied thereto will have suflicient force to compress the compression spring H after the brake shoe is moved into engagement with the rail 2, with the result that the piston I will move down into engagement with the lower end of the cylinder 6 which acts as a stop for the piston. The rod 8, the spring I I and the other members employed to connect the piston 'I with the brake shoe I are proportioned so that when the piston I is moved into engagement with the lower end of the cylinder 6 the spring II will be only partially compressed. As a result, when the track shoe is moved along the rail any vibrations of the track shoe caused by irregularities or rough spots in the track will be absorbed by the spring, which serves as a cushion, and will not be transmitted to the car truck.

This construction also operates to limit the amount of force which will be applied to the track shoe to hold it in engagement with the rail. This will be the force which is required to par tially compress the spring II, and this force will be substantially the same regardless of the pres sure of the fluid in the cylinder 6 as an increase in the pressure in the cylinder 6 will merely cause the piston I to be pressed against the lower end of the cylinder 6 more firmly and will not cause the spring II to be compressed to a greater degree. The force which is transmitted through the spring II is of suiiicient magnitude to insure that the track shoe will be moved into engagement with the rail, but is of small enough value that there is no objectionable tendency for the fluid pressure operated devices to lift the vehicle away from the rails.

The lower end of the rod 8 loosely fits in the opening in the upper end of the spring cage I0 so that a limited amount of movement is permitted between the spring cage l0 and the rod 8, and as a result the track shoe I can move a limited distance either longitudinally or transversely of the vehicle without effecting movement of the piston I. As pointed out above the spring acts as a cushion and permits the shoe I to move a short distance vertically without moving the piston 1.

A switch device for controlling the circuit to the brake shoe magnet winding is also provided, and as shown in the drawing, comprises a casing 20 containing a piston 2|. adapted to seat on a seat rib 22, the space within the seat rib being connected to the pipe I5.

A coil spring 23 urges the piston 2| to its seat. A vent passage 24 connects the chamber 25 outwardly of the seat rib 22 with the chamber 26 on the spring side of the piston 2| to prevent possible build up of fluid pressure in said chamber by leakage while the piston is in its seated position. The chamber 26 is connected to the atmosphere by way of thepassage 21.

The piston 2| is provided with a stem 30, carrying at its outer end, a switch contact 3| adapted when moved to the right from the position shown in the drawing to connect contacts 32 and 33 to close a circuit from a source of current, (not shown), through the winding of the track shoe I.

In operation, when it is desired to effect an application of the magnetic brake the operator supplies fluid under pressure to the pipe I5 which flows to the cylinder 6 and forces the piston I downwardly. Movement of the piston 'I is transmitted through the spring II to the brake shoe which is forced downwardly against the springs 4 so as to be yieldingly pressed into engagement with the rail 2.

The switch device for controlling the circuit to the winding of the brake shoe magnet is also open to the pipe I5, but owing to the restricted area of the piston 2| which is subject to the pressure in the pipe I5, when the piston is seated, and the resistance of the spring 23, the piston 2| will not move until the pressure of the fluid in the pipe I5 has built up to a relatively high value, which will be great enough to cause the piston I to shift the brake shoe I into engagement with the rail.

When the pressure of the fluidin the pipe I5 increases sufficiently to cause the piston 2| to move away from the seat rib 22 and expose the full area of the piston 2| to the fluid pressure supplied through the pipe |5 the piston is quickly shifted to the right so as to complete the circuit to the winding of the brake shoe, and also to move a seat rib 28 on the piston 2|. into engagement with a sealing gasket 29 clamped between the casing section 20 and the adjoining casing section so as to cut off the escape of fluid under pressure from the pipe I5 to the atmosphere by way of the passage 21. As the shoe is already in engagement with the rail beforecurrent is supplied to the track shoe winding the shoe will be in motion at the time at which it is energized and this insures that the brake shoe will not be heavily energized when the brake shoe engages the rail so that the initial application of the brake will be effected very smoothly.

When it is desired to release the magnetic brake, fluid under pressure is released from the pipe I5 thereby causing a reduction in the pressure acting on both pistons I and 2|. On a reduction in the pressure acting on the piston I this piston moves upwardly due to the expansion of the partially compressed spring I The track shoe, however, remains in engagement with the rail as it is energized, and its attraction for the rail holds it in engagement with the rail' against the springs" 4 which tend to lift it away from the rail. When the pressure in the pipe I5 has been reduced to a predetermined value the piston 2| is moved by the spring 23 to engage the seat rib 22. This.

movement of the piston 2| causes the switch con-' tacts 3| to move to the. left out of engagement with the contacts 32 and 33 so as to open the circuit to the winding of the track shoe. The winding thus being deenergized the magnetic attrac-,.,

tion of the shoe for the track decreases and the springs 4 then lift. the shoe to its upper or release position, where the shoe is yieldingly held against the stops or brackets 40 which project from the vehicle truck frame 3 and engage the upper face,

of the track shoe.

While one illustrative embodiment of the invention has been described in detail it is not my intention to limit its scope to that embodiment-or otherwise than by the terms of the following claims.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In a vehicle brake, a magnetic brake shoe normally held out of engagement with a rail, an'

abutment movable responsive to variations in fluid pressure, means to limit the amount of movement of said abutment, means interconnecting the abutment and the brake shoe whereby the shoe is movable into engagement with the rail by said abutment, said means including resiliently yieldable means through which movement of the abutment is transmitted to the shoe, means associated with said abutment and enigageable with said limiting means on movement of the abutment to a position to efiect engagement of the track shoe with the rail, the resiliently yieldable means being arranged to yieldingly connect the brake shoe and the abutment when the abutment is held by said limiting means, whereby movement of the brake shoe responsive to irregularities in the track are absorbed by said resilient means.

2. In a vehicle brake, a magnetic brake shoe, means to suspend the brake shoe above a rail, a

fluid pressure operated device for effecting movement of the shoe into engagement with a rail, said device comprising a movable abutment subject on one side to the pressure of the fluid in a chamber, yielding means comprising a pair of members and a compression spring positioned therebetween, one of said members being connected to the movable abutment, the other of said members being connected to the brake shoe, said members being urged together to effect compression of said spring on an increase in the pressure of fluid supplied to the chamber in the fluid pressure operated device upon movement of the brake shoe into engagement with the rail, and

means to limit movement of the abutment whereby the movement of the members of the yielding means is limited to an amount insuflicient to compress the spring to the closed position.

CLYDE c. FARMER- 

